A high court in Kiev rejected an appeal filed by Tymoshenko's defense team. She was sentenced last year after a conviction on charges she abused her authority during 2009 negotiations with Russian energy company Gazprom. Her counsel wanted the charges thrown out because of a lack of evidence.

Victoria Nuland, a spokeswoman for the U.S. State Department, expressed concern the charges against Tymoshenko and other opposition leaders were politically motivated.

We're not just talking about a singular event here," she said. "We're talking about the whole way justice has been applied in these cases and our concern that they are politically motivated and not rooted firmly in Ukrainian law."

Former Interior Minister Yuriy Lutsenko, a Tymoshenko ally, is serving a four-year prison on embezzlement charges.

Tymoshenko's attorneys said they'd take the case to European courts. The European Union said trials for opposition leaders in Ukraine didn't met international standards for "fair, transparent and independent legal processes."

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